1. Field of the Invention
This invention relates to guided missiles with air-breathing rocket motors, and more particularly to a control actuation system (CAS) for manipulating tail fins to maneuver the guided missile.
2. Description of the Related Art
Flight vehicles such as self-propelled missiles, gun or tube launched guided projectiles, kinetic interceptors and unmanned aerial vehicles require command authority to maneuver the vehicle to perform guidance and attitude control. Each of these vehicles may operate over a speed range encompassing both subsonic and supersonic Mach numbers and within the atmosphere and exo-atmosphere during a single mission. The differing speed and atmospheric conditions present different problems for effectively maneuvering the vehicle under volume, weight and cost constraints imposed by the vehicle and mission.
One approach used in a majority of if not all missile products employs a Control Actuation System (CAS) for guidance to the target. Typically the CAS employs a set of four fin control surfaces actuated by individual motors. The motor drives an input gear train that actuates an output gear that is coupled to a radially oriented fin control surface. Actuation of the fin control surfaces into the onrushing free stream produces drag and directional forces to maneuver the vehicle. Control surfaces are effective at supersonic speeds above Mach 1 in an atmosphere where sufficient drag and force is produced to quickly maneuver the vehicle.
An air-to-air missile (AAM) is a guided missile fired from an aircraft for the purpose of destroying another aircraft. AAMs are typically powered by one or more rocket motors, usually solid fueled but sometimes liquid fueled. Air-breathing rocket motors such as a ramjet are emerging as propulsion systems that will enable medium-range missiles to maintain higher average speeds across their engagement envelopments and achieve higher ranges.
In a typical rocket motor, there exists sufficient volume in the annular region between the exhaust tube and the missile airframe to locate the CAS. Typically, four tail fins are oriented radially about the circumference of the missile and spaced 90 degrees apart. The CAS includes four direct actuation assemblies positioned in the annular region within the missile airframe under the fin. A rotary drive motor drives an input gear train that rotates the output gear on which the tail fin is mounted to pivot the fin about its axis.
In guided missiles with air-breathing rocket motors, and in particular ramjet engines, the exhaust tube is contracted only slightly from the diameter of the rocket motor and substantially fills the cross section of the missile airframe. Air-breathing rocket motors operate with relatively low operating pressures and thus require relatively large flow cross sections through the exhaust tube. Consequently, a conventional CAS cannot be located within the missile airframe.
U.S. Pat. No. 5,904,319 entitled “Guided Missile with Ram Jet Drive” describes a CAS for use with a guided missile with ram jet drive. The missile has two outer air intakes in the lower area of the airframe, which lead to the tail with wake shafts, with a tail plane including four separately pivotable vanes in the form of a diagonal cross. A rigid wing arrangement is provided in or in front of the center of the missile. One drive unit with linear movement is provided for each vane. Two of the drive units are arranged longitudinally offset in the longitudinal and circumferential directions of the guided missile in each wake shaft. A kinematic connection from the drive unit to the lower vane is formed by a coupling rod each with joints at both ends. A kinematic connection from the drive unit to the upper vane is formed by a pivotable double lever each and a coupling rod with ball joints at both ends. This configuration produces non-linear (non-constant) gear ratio to pivot the vanes (see col. 4, line 43).